The present invention relates to the use of alkylaromatics and alkylcycloparaffins in Fischer Tropsch lube base oils to provide improved yields, as well as to provide moderate improvements in the physical properties of the oil.
Finished lubricants used for automobiles, diesel engines, and industrial applications consist of two general components: a lube base oil and additives. In general, a few lube base oils are used to generate a wide variety of finished lubricants by varying the mixtures of individual lube base oils and individual additives. Typically, lube base oils are simply hydrocarbons prepared from petroleum or other sources. Lube base oils are valuable commodities and are treated as essentially items of commerce. As items of commerce, they are bought, sold, and exchanged.
The majority of lube base oils used in the world today are derived from crude oil. There are several limitations to using crude oil as a source. Crude oil is in limited supply; it includes aromatic compounds that may be harmful and irritating, and it contains sulfur and nitrogen-containing compounds that can adversely affect the environment, for example, by producing acid rain.
Lube base oils can also be prepared from natural gas. This preparation involves converting the natural gas, which is mostly methane, to synthesis gas, or syngas, which is a mixture of carbon monoxide and hydrogen. An advantage of using products prepared from syngas is that they do not contain nitrogen and sulfur and generally do not contain aromatic compounds. Accordingly, they have minimal health and environmental impact.
Fischer-Tropsch chemistry is typically used to convert the syngas to a product stream that includes lube base oils, among other products. These Fischer Tropsch products have very low levels of sulfur, nitrogen, aromatics and cycloparaffins. The Fischer Tropsch derived products are considered environmentally friendly. Although environmentally desirable, only a small fraction of the world""s lube base oil supply is derived from Fischer Tropsch derived products. In addition, even though the properties of Fischer Tropsch derived lube base oils may make them environmentally friendly, the physical properties of these highly paraffinic lube base oils may in some respects limit their use. For example, due to their high paraffin content, Fischer Tropsch lube base stocks may exhibit poor additive solubility. Lube base additives typically have polar functionality; therefore, they may be insoluble or only slightly soluble in highly Fischer Tropsch lube base stocks.
To address the problem of poor additive solubility in highly paraffinic base stocks, various co-solvents, such as synthetic esters, are currently used. However, these synthetic esters are very expensive, and thus, the blends of the highly paraffinic Fischer Tropsch lube base oils containing synthetic esters, which have acceptable additive solubility, are also expensive. The high price of these blends limits the current use of highly paraffinic Fischer Tropsch base oils to specialized and small markets.
Therefore, there is a need for efficient and economical methods of increasing the yield of lube base oils from Fischer Tropsch facilities. In addition, there is a need for methods to improve certain physical properties, such as additive solubility, of highly paraffinic Fischer Tropsch lube base stocks to make their use more widespread and economical. The present invention provides such a method.
One aspect of the present invention relates to a lubricant comprising: a) at least one highly paraffinic Fischer-Tropsch derived lube base stock having a viscosity of greater than 3 cSt when measured at 40xc2x0 C., having a branching index of less than 5, and having an average length of alkyl side branches of less than 2 carbon atoms; and b) at least one lube base stock composed of alkylaromatics, alkylcycloparaffins, or mixtures thereof and having a viscosity of greater than 2 cSt when measured at 40xc2x0 C. The resulting lubricant comprises component b) in an amount between 1 wt % and 50 wt %, and the lubricant has viscosity of greater than 3 cSt when measured at 40xc2x0 C. The lubricant of the present invention may further comprise: one or more tube base oil additives and an effective amount of synthetic ester co-solvent to reduce turbidity of the lubricant to below two. The effective amount of ester co-solvent in the lubricant is less than the amount that would be required to reduce the turbidity to below two if the lubricant did not contain component (b).
An additional aspect of the present invention relates to an integrated process for producing highly paraffinic Fischer-Tropsch lube base stocks, alkylaromatics boiling in lube base oil range and/or an alkylcycloparaffins boiling in the lube base oil range. This process preferably involves the utilization of feedstocks obtained from a Fischer-Tropsch process.
In another aspect of the present invention, an integrated process for preparing a blended lube base oil is provided. The process comprises the step of blending (i) at least one Fischer-Tropsch derived lube base stock having a viscosity of greater than 3 cSt when measured at 40xc2x0 C. and having a branching index of less than 5 and (ii) at least one lube base stock composed of alkyaromatics, alkylcycloparaffins, or mixtures thereof and having a viscosity of greater than 2 cSt when measured at 40xc2x0 C. This process preferably involves the utilization of feedstocks obtained from a Fischer-Tropsch process.
In yet another aspect of the present invention, a process for increasing the yield of lube base oil from a Fischer Tropsch facility is provided. This process comprises performing Fischer-Tropsch synthesis on syngas to provide a product stream and fractionally distilling the product stream and isolating a C20+ fraction, a light aromatics fraction, and a light Fischer Tropsch products fraction containing olefins, alcohols, and mixtures thereof. The light aromatics fraction is alkylated with the light products fraction to provide an alkylaromatics fraction. Products from both the C20+ fraction and the alkylaromatics fraction are blended after optional further processing to provide a lube base oil. By using products prepared from the C20+ fraction and the alkylaromatics in the lube base oil, the overall yield of lube base oil from the Fischer Tropsch facility is increased.
A further aspect of the present invention relates to an integrated process for preparing a blended lube base oil. This process comprises subjecting light Fischer Tropsch products containing olefins, alcohols, or mixtures thereof to alkylation under catalytic alkylation conditions to form an alkylated stream and subjecting the alkylated stream to distillation to obtain alkylaromatics boiling in the lube base oil range and reformable Fischer Tropsch products. This process further comprises subjecting Fischer Tropsch derived wax to hydroisomerizing conditions to form highly paraffinic lube base stock. In this process the alkylaromatics and the highly paraffinic lube base stock are blended to form the blended lube base oil.
In another aspect of the present invention, an integrated process for preparing a blended lube base oil is provided. This process comprises subjecting light Fischer Tropsch products containing olefins, alcohols, or mixtures thereof to alkylation under catalytic alkylation conditions to form an alkylated stream and subjecting the alkylated stream to distillation to obtain alkylaromatics boiling in the lube base oil range and reformable Fischer Tropsch products. The process may further comprise subjecting the reformable Fischer Tropsch products to reforming under catalytic reforming conditions to form a light aromatic stream that may be recycled to the alkylation zone to form additional alkylaromatics boiling in the lube base oil range. Optionally a portion of the alkylaromatics boiling in the lube base oil range obtained from the distillation may be subjected to hydrogenation under catalytic hydrogenating conditions to obtain alkylcycloparaffins boiling in the lube base oil range. The process also comprises subjecting Fischer Tropsch derived wax to hydroisomerizing conditions to form highly paraffinic lube base stock. In this process, the highly paraffinic lube base stock is blended with the alkylaromatics and optionally the alkylcycloparaffins boiling in the lube base oil range to form the blended lube base oil.